Electron beam discharge device



Nov. 17, 41959` J. G. TUCKER ELECTRON BEAM DISCHARGE DEVICEv Filed March4, 1957 FIG-.2.

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TARGET ELEOTRON SOURCE R M Rw Y N OT D m. o G WL T L WE B W H E J W mSOURCE ELECTRON l 2,913,617 Y ELEcrnoN BEAM DISCHARGE` DEvrcE Jewell G.Tucker, Owensboro, Ky., assignor `tofGfenel-al :Electric Company, acorporation of New Yorlr This invention relates to electron dischargedevices of the electron beam type. c i

In many electron discharge devices the electron ow from the cathode` orelectron source to the anode or target electrode is confined to abeam-likepath. Along this path are disposed an accelerating electrode,positively biased with resect to the cathode and situated betweenthe-cathode and anode in a position to attract electrons from thecathode toward the anode, anda focus electrode, positioned between theaccelerating electrode and cathode and biased at or near cathodepotential for the purpose of converging electrons flowing from thecathode to the anode into a beam. Examples of such discharge devices arereceiving tubesof the beam or sheet beam type and cathode-ray tubes..Particularly at the higher frequencies, the quality of performance ofsuch devices is determined to a large extent by the proportion ofelectrons leaving the cathode ,which arrive at the anode, and, whereamplificationis desired and a control grid is employed, by the controlIgrid-anode transconductance and the ratio of transconductanceto cathodecurrent. Minimum electron flow from the cathode to electrodes'other thanthe anode is also important'where operation at a low noisefactor isdesired.

Accordingly, a principal object of the present invention is to providean electron discharge device of the electron beam type having improvedperformance in comparison with prior art devices, yet having asubstantially simplified structural-form affording significant savingsin manufacturing cost.` Y, i i

Another object is to provide an improved electron .discharge deviceofthe beam 4type characterized by `low noise factor ope/ration',substantially increased` control grid-anode transconductance,` j and `asubstantially increasedf'ratio of transconductance tocathodecurrent.i

.Another object is to provide, in an electron discharge device ofthe-electron beamftype having between the cathode and anode` a controlgrid, focusing electrode means, and laccelerating electrode means, animproved electrode structure enabling a substantial reduction incathode-accelerator spacing without objectionable `electron flow to theaccelerator means. i

These, and other objects of the present invention will be apparent fromthe following description taken in conjunction wit'h the accompanyingdrawing, and the scope of the invention will be defined in the appendedclaims.

l 2,913,617 Patented Nov. 17, 1959 voltage gradient, and focusing actionsuicient to give a well defined electron beam is maintained while thenonconducting covering on the accelerating electrode minimizesaccelerator current for low noise operation. In another `form of theinvention, the focus electrode and accelerating electrode are arrangedto form the outer layers'of a sandwich of which the middle layer` is asheet of electrically non-conductive material; therebyminimizing-accelerator-cathode spacing consistent with permissib leinter-electrode voltage gradient.

In the drawing: c

Fig. 1 is a partially broken away perspective View of an electrondischarge device of the electron beam type constructed in accordancewith one form of the present invention;

Fig. 2 is an enlarged fragmentary view of the device of Fig. 1, showingin transverse section the velectrode structure thereof, andpshowingschematically exemplary circuit connections thereof;-

. Fig. 3 is a view similar to Fig. 2, showing the electrode structuremodified in accordance with another form of the invention; Fig. 4 is adiagrammatic view of another electrode arrangement to which the present,invention may be Fig. 5 is a `view similar'to Fig. 4 showing theapplicaj tion of the present invention thereto.

Referring to Figs. 1 and 2, one embodiment of the invention isillustrated in connection with a discharge device of thefsheet beamtypey wherein the electronilow from the cathode to the anode is confinedto a beam having a relatively narrow horizontal dimension in comparisonwithV its vertical dimension. The discharge device of Fig. 1 includesanA enveloperZ enclosing a centrally located indirectly heatedcathode-4. The cathode may have one ormore electron emissive surfaces,that shown having two in number, referenced as 6 and 8, and facing inopposite directions.` Surrounding the cathode in spaced relation-therewith is a control `grid 10 constituting of a somewhat flattenedhelix of spacedturns of newire wound on a pair of supporting rods 12,14.A The remain- Briefly, according to one aspect of vthe invention, Iprovide an electron discharge device of the electron beam type in `whichthe separate focus electrode of the prior art is eliminated and itsfocusing action is suppliedby the accelerating electrode, theaccelerating electrode being modified for this purpose by minimizing itsspacing from ing electrode structure consistsof groups of electrodes,each disposed opposite one of the emissiveysurfaces` of the cathode.Each such group of electrodesincludes an anode 16, a planar focuselectrode 18 having one or more electron windows orapertures 20 betweenthe control grid 10 and anode 16 dimensioned according to the desiredsize and shape of the Velectron beam, anda planar acceleratorelectrode.22 situated between the focus electrode 18 andfanode 16 and having oneor moreapertures ,24 drmensioned according to the desired sizeand rshapeof the focused-electronv beam. :In thev discharge device shown, theanodes 16 arevfelectrically connected by a conductor shown'schematicallyat 26 in Fig. 2, the acceleratorY electrodes 22arelikewise connected by a conductor 28, and the focus electrodesflSare. likewise connected by:` conductor 30.' Theseveral electrodes aresupported between insulating spacers` 32, 34 which maybe of mica,andwhich engage the ,wall ofenvelope 2. j,

Exemplary circuit connections for. the electrodes of the dischargedevice of Figl are best'shown in Fig. 2. The anodes 16 are connected toa source of suitable positive.D.C. potential 36. The acceleratorelectrodes 22K are biased at'or near anode supply potential byfa suit?able dropping resistor 38, wconnected betweenelectrodes 22 and source36, and a bypass capacitor 40 connected between resistor 38 and ground.'Ihe focus electrodes` 18 are biased at the potential of cathode 4,which is connected to ground through resistorc42. ControlV grid :10receives signals through a coupling capacitor 44,V and a A 5 resister.,46i$ccnncted between .grid ,lofaml ground.. ance Without creating anobjectionable inter-electrode In normal operation of the dischargedevice of Figs. 1

scribed, it is desirabler to have a high control grid-anodetransconductance in order to providel adequate gain, and the anode,accelerating electrode and focus electrode currentsl should be as smallas possible in order to achieve a low noise factor.Y Small focus andaccelerating electrode currents have been difcult to obtain in dischargedevices ofthe prior art, however, because the requirement for formationof an electron beam of the necessary definition, electron density, andhomogeneity necessitates the placement of the electron-opaque portionsofk the focus electrode in the path of some of the electrons emanatingfrom the cathode, and requires the edges of the accelerating electrodeaperture 24 to closely surround the path of the electron beam, so thatsome electrons inevitably land on the focus and accelerating electrodes.Also, if the ,focus and accelerator electrode apertures 20 and 24 arenot in exact alignment, the accelerator will attract an abnormal numberof electrons, or if the acceleration aperture 24 has a small burr, itwill attract an abnormal number of electrons. This increase inaccelerator current in turn increases the partition noise and lowers thegrid-anode transconductance. Moreover, in prior art tubes theaccelerating electrode and focus electrode are independently supportedin spaced relation, and the transconductance is limited by the lowvintensity of the accelerator electrode field at the cathode, which isin turn caused by the necessity of spacing the accelerating electrode asuflicient distance from the cathode to avoid excessive voltagegradients between control grid, focus electrode and acceleratingelectrode.

These limitations on improved performance are `avoided, according to oneaspect of the present invention, by having each focus electrode- 18 andits associated accelerator electrode 22 of Figs. 1 and 2 constitute theouter layers of an integrated structure of sandwich construction, ofwhich the center layer consists of a sheet or plate of electricallynon-conductive material 50. Nonconductive sheet 50 is suitably aperturedas at 48 to coincide with electrodes 18 and 22, and preferably shouldhave a high dielectric constant so that it may be quite thin. The sheet50 may provide the principal mechanical support for the integratedsandwich structure, and may be, for example, a thin sheet of mica, whileelectrodes 18 and 22 need not be self-supporting, and may be of metalfoil or conductive paint clad or coated on layer 50. An importantadvantage of this construction is that the spacing of Vthe acceleratingelectrode 22 and cathode 4 is minimized because the interposition of thehigh dielectric layer 50 Vpermits accelerating electrode 22 and focuselectrode 18 to be spaced much closer together, in comparison withprior'art devices, without an objectionably largeinter-electrode voltagegradient; The intensity of the accelerating electrode field at thecathode is thereby substantially increased, with Va correspondingincrease in control grid-anode transconductance.

Further, in accordance with the invention, it has been discovered thatan additional substantial increase in transconductance can be. obtainedwhile maintaining good beam focusing action by eliminating altogetherthe conductive layer 18 which serves as the focus electrode in Fig. 2and moving the resulting two-layer electrode structure 5.0, 22 as closeto the cathode 4 as the limit of inter-electrode voltage gradientpermits. The resulting structure is shown in Figure 3, which illustratesanother form of the invention. In the discharge device of Fig. 3 theelectrode structure disposed between the control grid and each anode 16consists solely of a sheet or plate of electrically non-conductivematerial 64, provided with one or more suitable beam-forming apertures62, and

faced on the surface thereof facing the anode with a layer of conductivematerial 60 forming the accelerating electrode. Sheets 60 and 64 may bemutually mechanically supporting, or either may have the necessarystiffness to provide suitable mechanical support for the other.

With respect to the electrode structure of Fig. 3, it is an importantadvantage that the spacing between the accelerating electrode 60 andcathode 4 is further reduced in comparison with Fig. 2 without creationof an excessive voltage gradient between electrodes, because the surfaceof the composite structurel 60, 64 which faces the cathode consistssubstantially exclusively of electrically non-conducting material 64. Inone discharge device constructed according to the invention, forexample, it was found that accelerating grid-cathode spacing could bereduced by as much as fifty percent, in comparison with correspondingprior art types. Accordingly, with such a construction, the controlgrid-anode transconductance is maximized. Surprisingly, the resultingsignificant increase in gain is achieved at substantially no cost inincreased accelerating electrode current and noise factor, as measuredby static performance figures. In one exemplary embodiment constructedaccording to the form of the invention shown in Fig. 3, for example,lthe ratio of transconductance to cathode current as measured by staticperformance figures was of the order of 2000 micromhos per milliampere,Whereas in prior art beam-type discharge devices this ratio is normallyless than 1000 micromhos per milliampere, The reason for this net gainin performance is not yet fully understood, but it is believed that theaccelerating electrode 60, when positioned so close to the cathode, isable to provide some focusing effect as well as the desired acceleratingeffect, and it is also believed that under electron bombardment thenon-conducting layer 64 charges to a negative potential, relative to thecathode, and thus exerts an effective focusing action on the electroncam. Accelerating electrode current is not objectionably increasedapparently because the non-conducting layer 64 effectively shields theaccelerating electrode 60 from electrons traveling from the cathodetoward the anode, and once such electrons pass through the opening 62 inthe accelerating electrode, they are traveling at suicient velocity andare formed into such a well-defined beam that very few, if any, deviatefrom the beam path enough to land on the accelerating electrode 60.

While the invention has been illustrated and explained in connectionwith an electron discharge device of the sheet beam type, it will bereadily understood by those skilled in the art that the invention isequally applicable to other types of discharge devices, or in fact toany electrode arrangement wherein electrons are drawn from a source byan accelerating electrode past an intermediate focus electrode whosefunction it is to converge the electrons into a beam. Fig. 4 shows sucha generalized environment, including an electron source 70, target 72,accelerating electrode 74 having one or more apertures 75, and spacedfocus electrode 76 having one or more beam forming apertures 80, whilethe application of the presentl invention to such an environment isshown in Fig. 5. Inl the structure of Fig. 4 the focus electrode 76 andaccelerating electrode 74 are separate and independent, the acceleratingelectrode is maintained by a bias supply, illustrated at potentiometer78, at a substantially higher potential than the focus electrode 76 soas'to create the necessary electrostatic field therebetween for goodfocusing of electrons passing through the beam forming aperture 80, andthe two electrodes 74, 76 are spaced apart a suliicient distance toavoid the establishment of an excessive voltage gradient therebetween.In the structure of Fig. 5, however, in accordance with the presentinvention, the separate focus electrode 76 is completely eliminated andthe accelerating electrode is faced on its surface facing the electronsource 70 with a layer of electrically non-conductive material 82. Thenonconductive surface 82 enables the accelerating electrode 74 andelectron source 70 to be spaced much closer without creating anexcessive voltage gradient between them, thereby maximizing theintensity of the accelerating field at the electron source 70. Also,like llayer 64 in Fig. 3, non-conducting layer 82 effectively focusesthe electrons passing through aperture 75 into a well-defined beam ofdesired homogeneity and density, yet the shielding action ofnon-conducting layer 82 minimizes current to the accelerating electrode74.

It will be appreciated by .those skilled in the art that the inventionmay be carried out in various ways and may take various forms andembodiments other than those illustrative embodiments heretoforedescribed. It is to be understood, therefore, that the scope of theinvention is not limited by the details of the foregoing description,but will be defined in the following claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. In an electron discharge device of the electron beam type, anelectron source, an electron target, and a composite focusing and-accelerating electrode disposed between the source and target, saidcomposite electrode comprising a sheet of electrically conductingmaterial situated in and transversely disposed with respect to the pathof electron fiow from the source to the target, said sheet of conductingmaterial having a single aperture therein through which electrons areadapted to flow and adapted to be maintained at an electron acceleratingpotential with respect to the source, and a covering of non-conductingmaterial on the side of said conducting sheet facing said source, saidcovering extending over the entire surface of said sheet of conductingmaterial facing said cathode and having a single aperture the peripheryof which is coincident with the periphery of the aperture in the sheetof conducting material.

2. In an electron discharge device of the electron beam type, a cathode,an anode, and a composite focus and accelerating electrode disposedbetween the cathode and anode, said composite electrode comprising asandwich consisting of a sheet of electrically non-conducting materialsituated in and` transversely disposed with respect to the path ofelectron fiow from the cathode to the anode, said sheet ofnon-conducting material having an aperture therein through 'whichelectrons are adapted to iiow, and a layer of electrically conductingmaterial on the surface of said non-conducting sheet facing said anodesaid non-conducting material covering all portions of the surface ofsaid conductive layer facing said cathode, said layer of `conductingmaterial being adapted to be maintained at an electron acceleratingpotential with re* spect to the cathode. y

3. In an electron discharge device of the electron beam type, a cathode,an anode, an accelerating electrode comprising a sheet of electricallyconductive material transversely disposed between the cathode and anodeand adapted to be maintained at a positive potential with respect to thecathode for promoting electron flow from the cathode to the anode, saidaccelerating electrode having an aperture through which electronsflowing from the cathode to the anode are adapted to pass, and a layerof electrically non-conducting material covering only the entire surfaceof said sheet of conductive material facing said cathode, saidnon-conducting material extending to coincidence with the periphery ofsaid aperture being adapted to build up an electron charge responsive tobornbardment by electrons emitted from said cathode, whereby theelectrostatic field associated with said charge in the vicinity of saidaperture in said accelerating electrode exerts a converging and focusinginfluence-forming electron flowing through said aperture into a beam.

4. In an electron discharge device of the electron beam type, a cathode,an anode, and a composite electrode for accelerating and focusingelectron flow from said cathode of said anode, said composite electrodecomprising a sheet of electrically non-conducting material situated inand transversely disposed with respect to the path of electron flowbetween the cathode and anode and having a single aperture through whichelectrons may pass, and a layer of conductive material on each face ofsaid sheet of non-conducting material, each layer of conductive materialhaving a single aperture coincident with the single aperture in saidnon-conducting sheet and coincidently covering the entire surface ofsaid non-conducting sheet about the aperture therein.

5. In an electron discharge device of the electron beam type, a cathode,an anode, a control grid between the cathode and anode, and a compositefocus and accelerating electrode disposed between the control grid andanode, said composite electrode comprising a sheet of electricallynon-conducting material situated in and transversely disposed withrespect to the path of electron fow from the cathode to the anode andhaving an aperture therein through which electrons are adapted to flow,a

Y first layer of conducting material on the side of said nonconductingsheet facing said anode adapted to be maintained at an electronaccelerating potential with respect to the cathode, said non-conductingmaterial masking the entire surface of said first layer facing saidcathode and said non-conducting material and first layer havingcoincident apertures, and a second layer of conducting material on theside of said non-conducting sheet facing said cathode adapted to bemaintained at a potential less than said first layer.

6. An electron discharge device comprising an envelope, a pair ofelectrically non-conducting discs supported within the envelope inspaced generally parallel relation, a cathode supported between thediscs having an electron emitting surface facing in a directiongenerally parallel to the plane of the discs, an anode supported betweenthe discs and spaced opposite the cathode, a con- Y trol grid supportedbetween the discs situated between the cathode and anode, a plate ofelectrically non-conducting material supported between the control gridand anode, said plate having an aperture through which electrons areadapted to ow from the cathode to the anode, and a layer of electricallyconductive material extending outwardly from the periphery of saidaperture on the surface of said plate facing said anode and adapted tobe maintained at an electron accelerating potential relative to saidcathode, said layer of conductive material being disposed in coincidentrelation on the entire surface of said plate of non-conducting materialand all portions of the surface of said conductive layer facing saidcathode being covered by said plate of non-conducting material.

7. An electron discharge device comprising an envelope, a pair ofelectrically non-conducting discs supported within the envelope inspaced generally parallel relation, a cathode supported between thediscs having an electron emitting surface facing in a directiongenerally parallel to the plane of the discs, an anode supported betweenthe discs and spaced opposite the cathode, a control grid supportedbetween'the discs situated between the cathode and anode, a plate ofelectrically non-conducting material supported between the discs andsituated between the control grid and anode, said plate having anaperture through which electrons are adapted to flow from the cathode tothe anode, a first layer of electrically conductive material on thesurface of said plate facing said anode and adapted to be maintained atan electron accelerating potential relative to said cathode, and asecond layer of electrically conductive material on the surface of saidplate facing said cathode, said non-conducting material covering all,portions of the surface of said first v conductive layer facing thecathode, said rst and second layers of conductive material each havingan aperture 7 8 the periphery of which is coincident with the peripheryof 2,686,885 Bailin Aug. 17, 1954 the aperture in the plate ofnon-conducting material. 2,712,087 'Fite et al. June 28, 1955 '2,735,032Bradley Feb. 14, 1956 References Cited in the le of this patent2,777,084 Laerty I an. 8, 1957 UNITED STATES PATENTS 5 FOREIGN PATENTS2,455,851 Beggs Dec. 7, 1948 707,064 Great Britain Apr. 14, 1954

